From 7ded429152e84831f6696585755f318fb351e67f Mon Sep 17 00:00:00 2001

From: Nicholas Piggin <npiggin@gmail.com>

Date: Wed, 14 Jun 2017 23:02:41 +1000

Subject: [PATCH] cpuidle: powerpc: no memory barrier after break from idle

References: PED-3947 bsc#1210544 ltc#202303

Patch-mainline: v4.13-rc1

Git-commit: 7ded429152e84831f6696585755f318fb351e67f

A memory barrier is not required after the task wakes up,

only if we clear the polling flag before waking. The case

where we have work to do is the important one, so optimise

for it.

Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Acked-by: Michal Suchanek <msuchanek@suse.de>

---

 drivers/cpuidle/cpuidle-powernv.c | 11 +++++++++--

 drivers/cpuidle/cpuidle-pseries.c | 11 +++++++++--

 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c

index 9d03326ac05e..37b0698b7193 100644

--- a/drivers/cpuidle/cpuidle-powernv.c

+++ b/drivers/cpuidle/cpuidle-powernv.c

@@ -59,14 +59,21 @@ static int snooze_loop(struct cpuidle_device *dev,

 	ppc64_runlatch_off();

 	HMT_very_low();

 	while (!need_resched()) {

-		if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time)

+		if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {

+			/*

+			 * Task has not woken up but we are exiting the polling

+			 * loop anyway. Require a barrier after polling is

+			 * cleared to order subsequent test of need_resched().

+			 */

+			clear_thread_flag(TIF_POLLING_NRFLAG);

+			smp_mb();

 			break;

+		}

 	}

 	HMT_medium();

 	ppc64_runlatch_on();

 	clear_thread_flag(TIF_POLLING_NRFLAG);

-	smp_mb();

 	return index;

 }

diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c

index a404f352d284..e9b3853d93ea 100644

--- a/drivers/cpuidle/cpuidle-pseries.c

+++ b/drivers/cpuidle/cpuidle-pseries.c

@@ -71,13 +71,20 @@ static int snooze_loop(struct cpuidle_device *dev,

 	while (!need_resched()) {

 		HMT_low();

 		HMT_very_low();

-		if (snooze_timeout_en && get_tb() > snooze_exit_time)

+		if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {

+			/*

+			 * Task has not woken up but we are exiting the polling

+			 * loop anyway. Require a barrier after polling is

+			 * cleared to order subsequent test of need_resched().

+			 */

+			clear_thread_flag(TIF_POLLING_NRFLAG);

+			smp_mb();

 			break;

+		}

 	}

 	HMT_medium();

 	clear_thread_flag(TIF_POLLING_NRFLAG);

-	smp_mb();

 	idle_loop_epilog(in_purr);

-- 

2.40.0